Integrator and image read device

Abstract

An integrator having a first circuit including an integrating capacitor and a feedback resistor, both being connected in parallel to each other in a negative feedback loop of the first circuit, and a second circuit, connected to an output side of the first circuit, for compensating for a leak by the feedback resistor. The first circuit operates as an integrator in high frequencies, and as a current-voltage converter in low frequencies. Further, the second circuit compensates for the leak by the feedback resistor, thereby to produce a value indicative of the result of integrating an input current.

What is claimed is: 
     
       1. An integrator comprising: a first circuit including an integrating capacitor and a feedback resistor, both being connected in parallel to each other in a negative feedback loop of said first circuit; and   a second circuit, connected to an output side of said first circuit, for compensating for a leak by said feedback resistor.   
     
     
       2. The integrator according to claim 1, wherein said first circuit is an amplifier of which the feedback portion includes a parallel circuit consisting of an integrating capacitor and a feedback resistor. 
     
     
       3. The integrator according to claim 1, wherein said first circuit comprises: a first amplifier of which the feedback portion includes an integrating capacitor;   a second amplifier for amplifying an output voltage of said first amplifier; and   a feedback resistor connected between an output side of said second amplifier and an input side of said first amplifier.   
     
     
       4. The integrator according to claim 1, wherein two compensating circuits are connected in parallel to the output side of said first circuit, and are alternately operated. 
     
     
       5. The integrator according to claim 1, wherein said second circuit comprises: a capacitor of which one end is connected to the output side of said first circuit and the other end is used as an output terminal;   a constant current source, connected to the other end of said capacitor, for producing a current substantially proportional to an output voltage of said first circuit; and   a reset switch connected to the other end of said capacitor.   
     
     
       6. An image read device comprising: a sensor with a current mode output;   a first circuit connected to said sensor, including an integrating capacitor and a feedback resistor, both being connected in parallel to each other in a negative feedback loop of said first circuit; and   a second circuit, connected to an output side of said first circuit, for compensating for a leak by said feedback resistor.